Information Technology Reference
In-Depth Information
7.9.4.1 OAIS and Emulation as a Preservation Strategy
OAIS does describe instruction emulation as possible method of preserving Access
Software (AS). In OAIS, AS refers to software that reads, processes and renders data
that is being preserved for a given designated community. It sees the preservation
of AS as necessary when the look (rendering) and feel of the software in important
to the reuse and understanding of the data being preserved and also when inade-
quate Representation Information is available that would allow the reproduction of
the software's capabilities. For example when software provides a unique plotting
method for data (rendering) or a unique and complex algorithm for processing the
data before it is rendered. Here, rendering could be a visual, audio or even a physical
rendering (plotting for example) of data.
When we talk about the “feel” of software we usually refer to the timing to which
things happen within the software. For example, the movement of a character in a
computer game may be required to happen in a smooth and uniform way for the
game to be played properly. Timing is usually related to the timing of the execution
of the instructions of the computers instruction set (they are executed at the appro-
priate time and for the right duration relative to the other instructions). An example
of where timing could prove to be a problem is in the playing of video and audio
data. If the instructions used by the software playing the audio or video are not
executed at the appropriate time then the audio or video could slow down or speed
up causing an unusual reproduction. Similarly, if some instructions took too long
to execute relative to the other instruction then a similar effect would be observed.
This is not the necessarily the same as the emulator simply running slowly so that
the whole recording is played in “slow motion”; lack of synchronisation may also
arise.
OAIS also states that the reimplementation of the functionality of software and
software APIs is an emulation technique. If adequate information is available about
the software, algorithms and rendering methods it uses, then software can simply
be re-implemented in the future. But OAIS points out that even then problems
may arise as documentation of the APIs may still not be enough to reproduce the
behaviour of the old software. This is because one can never be sure that the new
implementation behaves like the original unless the software has been tested and
its behaviour and output compared against the old software. This problem can be
overcome by recording any input and the corresponding output from the original
software and using it as test and comparison against the output of the new software
ensuring that the new implementation is correct.
7.9.4.2 Preserving Software with an Emulator
An important aspect of preserving software and data with an emulator is simply test-
ing to see if the emulator runs the software correctly (assuming that we are keeping
both the software and the emulator together for preservation). The software may
run slowly on the emulator, but as long as the look, feel, and accuracy is preserved
then this is one test we can do to ensure the software's correct and “trustworthy”
